You can use Code Card with something like
workflow.anyVar = Number(event.preview).toFixed(2)
Here the anyVars has to be where you want to store your result. So replace it with your var name
Number will convert the String into a number. In my case I type directly usign a Raw Input Card, that's why I use event.preview to get the user last input.
Finaly, the important part, toFixed(2) will round your number to 2 diget as you need. It round it, don't just cut it. so 19.56799 will be 19.57
Hopa that help